The present invention relates to an improved knife holder for a chipper disc or like apparatus for producing chips or flakes from a piece of wood.
It is common to form chips for producing wood pulp for use in the manufacture of paper products, employing apparatus known as chippers or choppers, and to produce flakes or wafers for use in the manufacture of waferboard or oriented strand board, employing similar apparatus known as waferizers and stranders. All of these apparatus employ a disc rotating in the vertical plane and having one or more knives attached to knife holders disposed so that cutting edges thereof extend beyond the face of the disc. A piece of wood is fed against the face of the disc and the knives, so that cuts are made in the wood, producing the chips or flakes. The knives experience very large forces and must be held firmly in place.
However, the knives must be removable from the knife holder, for reversing or replacing them. It has been a problem to ensure firm attachment of the knives while providing for their easy removal from the knife holders.
As a response, Holmberg et al., U.S. Pat. No. 4,694,995, proposes a knife holder that includes a filler piece fitting into a recess in the chipper disc, and a cassette for holding the knife. The cassette has a top and bottom part that clamps the knife therebetween and a fastener is inserted through the top and bottom parts that extends into the filler piece, but not into the chipper disc. The filler piece is separately fastened to the chipper disc. Though it is not explained in the patent, the filler piece is a relatively large and heavy component, while the top part is relatively small and light. It is proposed that the knife may be removed simply by removing the fastener for the cassette and by lifting the small, light top part, while the larger, heavier filler piece remains fixed to the chipper disc. It is also proposed that the fastener for the cassette may be loosened to remove the knife.
Whether the fastener for the cassette of Holmberg is removed entirely or merely loosened, the top part of the cassette and the knife become loose and at least the top part must be moved to get at the knife. As the knife is heavy and difficult to handle and it is desirable to be able to use two hands for this purpose, the aforementioned requirement imposed by Holmberg is objectionable. Moreover, to the extent that the fastener for the cassette of Holmberg is smaller and lighter, it is capable of exerting less force on the knife than prior art fasteners for knife holders so that the knife is not held as firmly.
Accordingly, there is a need for an improved knife holder for a chipper disc or the like that provides for easier removal of a knife held thereby while providing for more firmly holding the knife during operation of the apparatus.